The invention relates generally to ultrasonic frequency analysis and more specifically concerns ultrasonic frequency analysis which employs frequency tracked gated rf pulses.
In a typical prior art device for obtaining ultrasonic frequency analysis, a short untuned voltage spike from a pulser shock-excites a highly damped piezoelectric transducer. The transducer emits a sharp ultrasonic pulse with a relatively large frequency bandwidth which propagates through a delay line before striking the sample. The return echoes from two different regions of the sample are gated singly or together, depending on the properties to be investigated, into a spectrum analyzer which displays the magnitude of the Fourier transform of the input to the analyzer. In a similar but different prior art device the shock pulser is replaced by a gated rf source with a frequency centered at the resonant frequency of the transducer.
The disadvantages of the prior art devices are: there is modulation of the frequency spectra due to finite pulse widths; large amplitude drive voltages are required which produce nonlinearities in the signal emitted by the transducer and which contributes to the problem of electronic rise time and amplifier saturation; and errors are caused by receiver gate width or position.
It is therefore an object of this invention to eliminate modulation of the frequency spectra due to finite pulse widths in ultrasonic frequency analysis.
Another object of this invention is to lower the instantaneous drive power required for the transducers in ultrasonic frequency analysis, and thereby decrease the disadvantages associated with large amplifier drive voltages.
A further object of this invention is to decrease the errors due to receiver gate width or position in ultrasonic frequency analysis.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawings.